Programming Forums > Application Development > C++

Lakrids · Jun 8th, 2008, 12:44 PM

Hello everyone,

I am quite motivated to code a new programming language this summer. My idea is, given the source code of a program written in this language, to translate it to c/c++ and then compile it using gcc/g++. Now, before starting the project, I would like to know if there is a way to do this cross-platform. What I mean is :
1) On UNIX-like systems, you only have to do fork() and exec("g++ -o etc...")
2) On Wind@ws, I don't know of an exec()-like substitute SC, perhaps system(), but I'm not sure if I should use it.
What would be the correct way of doing this?

Thank you

titaniumdecoy · Jun 8th, 2008, 2:40 PM

I'm not sure, but popen might be what you're looking for.

Sorrofix · Jun 8th, 2008, 3:16 PM

>perhaps system(), but I'm not sure if I should use it.
Depends on what you need. system() pauses your program, opens a new shell, and executes the command you give it in its argument. When the program finishes executing, it will exit, the shell will close, and your program will resume execution.

popen, like titaniumdecoy mentioned, is for opening a pipe to a program. That is, it'll execute a program, and then you can use the pipe it's opened to communicate with the other process. In other words, your program isn't halted until the process is done (like system()).

grumpy · Jun 8th, 2008, 10:16 PM

There is no direct fork() equivalent under windows [creating a duplicate of the current process with the same state, except being able to detect it is forked] but it is possible to create a new process to execute a new program.

Libraries with some compilers (Microsoft, Borland) targeting windows do support an execl() function within a header named something like <process.h>.

Also look up the CreateProcess() function in the win32 API. execl() functions and system() functions under windows will typically be implemented using CreateProcess() or related functions.

titaniumdecoy · Jun 8th, 2008, 10:59 PM

You could use the pthread library, although I believe it requires a DLL on Windows.

Lakrids · Jun 9th, 2008, 7:55 AM

Thank you! I didn't know so much possibilities existed on Wind@ws! I will definately look up popen() and execl(). system() doesn't look like a very good choice, given that you can't communicate with your "child", e.g. you don't know when it has completed it's task or failed, and if so, for what reason.

Thanks for the help!

Sorrofix · Jun 9th, 2008, 10:47 AM

>you don't know when it has completed it's task or failed
system() waits until its child process has completed. Upon completion, system() will return the value returned by the child process. So yes, using the return value of system(), you can determine the success of the program you ran.

Lakrids · Jun 9th, 2008, 11:04 AM

Quote:

system() waits until its child process has completed. Upon completion, system() will return the value returned by the child process. So yes, using the return value of system(), you can determine the success of the program you ran.

Wow, I didn't know that! To be honest, the only time I used system() was back when I started learning C++ and I used system("pause") (they should really change those online tutorials

)...had no clue that it actually returned something!

So what does it return? An int?

titaniumdecoy · Jun 9th, 2008, 2:41 PM

man 3 system:

Quote:

If command is a NULL pointer, system() will return non-zero if the command interpreter sh(1) is available, and zero if it is not.

The system() function returns the exit status of the shell as returned by waitpid(2), or -1 if an error occurred when invoking fork(2) or waitpid(2). A return value of 127 meansmthe execution of the shell failed.

grumpy · Jun 9th, 2008, 3:39 PM

Quote:

Originally Posted by Sorrofix

system() waits until its child process has completed. Upon completion, system() will return the value returned by the child process. So yes, using the return value of system(), you can determine the success of the program you ran.

That is only true on some target platforms, and with some libraries. It is not a predictable result.

The C standard has this to say on system(), and is all that can relied upon in cross-platform development.

Quote:

Originally Posted by ISO/IEC 9899

7.20.4.6 The system function

Synopsis

1 #include <stdlib.h>
int system(const char *string);

Description

2 If string is a null pointer, the system function determines whether the host
environment has a command processor. If string is not a null pointer, the system function passes the string pointed to by string to that command processor to be executed in a manner which the implementation shall document; this might then cause the program calling system to behave in a non-conforming manner or to terminate.

Returns

3 If the argument is a null pointer, the system function returns nonzero only if a command processor is available. If the argument is not a null pointer, and the system function does return, it returns an implementation-defined value.

Jun 8th, 2008, 12:44 PM	#1
Lakrids Newbie Join Date: Dec 2007 Posts: 28 Rep Power: 0	Cross-platform exec() Hello everyone, I am quite motivated to code a new programming language this summer. My idea is, given the source code of a program written in this language, to translate it to c/c++ and then compile it using gcc/g++. Now, before starting the project, I would like to know if there is a way to do this cross-platform. What I mean is : 1) On UNIX-like systems, you only have to do fork() and exec("g++ -o etc...") 2) On Wind@ws, I don't know of an exec()-like substitute SC, perhaps system(), but I'm not sure if I should use it. What would be the correct way of doing this? Thank you

Jun 8th, 2008, 2:40 PM	#2
titaniumdecoy Expert Programmer Join Date: Nov 2005 Posts: 856 Rep Power: 3	Re: Cross-platform exec() I'm not sure, but popen might be what you're looking for.

Jun 8th, 2008, 3:16 PM	#3
Sorrofix Expert Bug Developer Join Date: Apr 2008 Posts: 21 Rep Power: 0	Re: Cross-platform exec() >perhaps system(), but I'm not sure if I should use it. Depends on what you need. system() pauses your program, opens a new shell, and executes the command you give it in its argument. When the program finishes executing, it will exit, the shell will close, and your program will resume execution. popen, like titaniumdecoy mentioned, is for opening a pipe to a program. That is, it'll execute a program, and then you can use the pipe it's opened to communicate with the other process. In other words, your program isn't halted until the process is done (like system()). Last edited by Sorrofix; Jun 8th, 2008 at 3:28 PM.

Jun 8th, 2008, 10:16 PM	#4
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,223 Rep Power: 5	Re: Cross-platform exec() There is no direct fork() equivalent under windows [creating a duplicate of the current process with the same state, except being able to detect it is forked] but it is possible to create a new process to execute a new program. Libraries with some compilers (Microsoft, Borland) targeting windows do support an execl() function within a header named something like <process.h>. Also look up the CreateProcess() function in the win32 API. execl() functions and system() functions under windows will typically be implemented using CreateProcess() or related functions.

Jun 8th, 2008, 10:59 PM	#5
titaniumdecoy Expert Programmer Join Date: Nov 2005 Posts: 856 Rep Power: 3	Re: Cross-platform exec() You could use the pthread library, although I believe it requires a DLL on Windows.

Jun 9th, 2008, 7:55 AM	#6
Lakrids Newbie Join Date: Dec 2007 Posts: 28 Rep Power: 0	Re: Cross-platform exec() Thank you! I didn't know so much possibilities existed on Wind@ws! I will definately look up popen() and execl(). system() doesn't look like a very good choice, given that you can't communicate with your "child", e.g. you don't know when it has completed it's task or failed, and if so, for what reason. Thanks for the help!

Jun 9th, 2008, 10:47 AM	#7
Sorrofix Expert Bug Developer Join Date: Apr 2008 Posts: 21 Rep Power: 0	Re: Cross-platform exec() >you don't know when it has completed it's task or failed system() waits until its child process has completed. Upon completion, system() will return the value returned by the child process. So yes, using the return value of system(), you can determine the success of the program you ran.

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Programming Forums > Application Development > C++

Cross-platform exec()